Based on the appearance thereof, a lithium secondary battery may be generally classified as a cylindrical battery, a prismatic battery, or a pouch-shaped battery. Based on the type of an electrolyte, a lithium secondary battery may be also classified as a lithium ion battery, a lithium ion polymer battery, or a lithium polymer battery.
A recent trend in the miniaturization of mobile devices has increased the demand for a prismatic battery or a pouch-shaped battery, which has a small thickness. In particular, much interest is currently focused on such a pouch-shaped battery because it is easy to modify the shape of the pouch-shaped battery, the manufacturing cost of the pouch-shaped battery is low, and the pouch-shaped battery is lightweight.
In general, a pouch-shaped battery is a battery having an electrode assembly and an electrolyte in a pouch-shaped battery case, made of a laminate sheet including a resin layer and a metal layer, in a sealed state. The electrode assembly mounted in the battery case may be configured to have a jelly-roll (wound) type structure, a stacked type structure, or a combination (stacked/folded) type structure.
FIG. 1 is a view typically showing the structure of a pouch-shaped secondary battery including a stacked type electrode assembly.
Referring to FIG. 1, a pouch-shaped secondary battery 10 includes an electrode assembly 30, electrode tabs 40 and 50 extending from the electrode assembly 30, electrode leads 60 and 70 welded to the electrode tabs 40 and 50, and a battery case 20, in which the electrode assembly 30 is mounted.
The electrode assembly 30 is a power generating element configured to have a structure in which positive electrodes and negative electrodes are sequentially stacked in a state in which separators are disposed respectively between the positive electrodes and the negative electrodes. The electrode assembly 30 is configured to have a stacked type structure or a stacked/folded type structure. The electrode tabs 40 and 50 extend from electrode plates of the electrode assembly 30. The electrode leads 60 and 70 are electrically connected to the electrode tabs 40 and 50 extending from the respective electrode plates, for example, by welding. The electrode leads 60 and 70 are partially exposed outward from the battery case 20. In addition, insulative films 80 are partially attached to the top and bottom of each of the electrode leads 60 and 70 to improve sealing between the electrode leads 60 and 70 and the battery case 20 and, in addition, to improve an electrically insulative state.
The battery case 20 is made of an aluminum laminate sheet. The battery case 20 provides a space in which the electrode assembly 30 is mounted. The battery case 20 is generally configured to have a pouch shape. In the stacked type electrode assembly 30 as shown in FIG. 1, the inner upper end of the battery case 20 is spaced apart from the electrode assembly 30 such that the positive electrode tabs 40 and the negative electrode tabs 50 can be coupled to the electrode leads 60 and 70, respectively.
In recent years, however, a new type of battery cell has been required in accordance with a trend change for a slim type design or various other designs.
In addition, the above-mentioned battery cell may be configured to include electrode assemblies having the same size or the same capacity. For this reason, in order to manufacture a battery cell having a new structure in consideration of the design of a device, to which the battery cell is applied, it may be necessary to reduce the capacity of the battery cell or modify the design of the device such that the size of the device is increased.
In order to solve the above-mentioned problems, battery cells having different sizes are stacked to a battery pack, which is disclosed in some prior arts. However, the battery pack is configured to have a structure in which the battery cells are stacked. For this reason, electrochemical reaction does not occur between the stacked battery cells. As a result, the thickness of the battery pack may be increased, and the capacity of the battery pack may be reduced due to the increased thickness of the battery pack
In addition, electrical connection may be complicated during modification of the design of the battery cell with the result that it may be difficult to manufacture a battery cell satisfying desired conditions.
Therefore, there is a high necessity for an electrode assembly applicable depending upon the shape of a device, to which a battery cell is applied, and a battery cell including the same.